Vesicular sequestration limits the buildup of toxic products of enzymatic and spontaneous oxidation of catecholamines. A vesicular storage defect therefore could play a pathogenic role in the death of catecholaminergic neurons in a variety of neurodegenerative diseases. In putamen, deficient vesicular storage is revealed in vivo by accelerated loss of 18F-DOPA-derived radioactivity and post-mortem by decreased tissue dopamine (DA):DOPA ratios; in myocardium in vivo by accelerated loss of 18F-DA-derived radioactivity and post-mortem by increased 3,4-dihydroxyphenylglycol:norepinephrine (DHPG:NE) ratios; and in sympathetic noradrenergic nerves overall in vivo by increased plasma F-dihydroxyphenylacetic acid (F-DOPAC):DHPG ratios. We retrospectively analyzed data from 20 conditions with decreased or intact catecholaminergic innervation, involving different etiologies, pathogenetic mechanisms, and lesion locations. All conditions involving parkinsonism had accelerated loss of putamen 18F-DOPA-derived radioactivity; in those with post-mortem data there were also decreased putamen DA:DOPA ratios. All conditions involving cardiac sympathetic denervation had accelerated loss of myocardial 18F-DA-derived radioactivity; in those with post-mortem data there were increased myocardial DHPG:NE ratios. All conditions involving localized loss of catecholaminergic innervation had evidence of decreased vesicular storage specifically in the denervated regions. Thus, across neurodegenerative diseases, loss of catecholaminergic neurons seems to be associated with decreased vesicular storage in the residual neurons. (Goldstein DS, Holmes C, Mash D, Sidransky E, Stefani A, Kopin IJ, Sharabi Y. Deficient vesicular storage: A common theme in catecholaminergic neurodegeneration. Parkinsonism Relat Disord 2015;21:1013-1022.) PD with orthostatic hypotension (PD+OH) can be difficult to distinguish clinically from parkinsonian form of MSA (MSA-P). Cardiac sympathetic neuroimaging by 18F-DAPET scanning efficiently separates these diseases, but this testing is not generally available. We assessed whether plasma biomarkers of a vesicular storage defect can separate PD+OH from MSA-P. After F-DA injection, augmented production of F-dihydroxyphenylacetic acid (F-DOPAC) indicates decreased vesicular storage, and we predicted that arterial plasma F-DOPAC would be elevated in PD+OH but not in MSA-P. We measured plasma F-DOPAC after 18F-DA administration in patients with PD+OH or MSA-P and in healthy control subjects. Peak F-DOPAC:DHPG was calculated, to adjust for effects of denervation on F-DOPAC production. All MSA-P patients had peak F-DOPAC:DHPG <60, in contrast with 9 of 12 PD+OH patients (p<0.0001). Adjustment of peak F-DOPAC for DHPG increased test sensitivity from 58% to 81% at similar high specificity. Thus, after F-DA injection plasma peak F-DOPAC:DHPG distinguishes PD+OH from MSA-P (Goldstein DS, Kopin IJ, Sharabi Y, Holmes C. Plasma biomarkers of decreased vesicular storage distinguish Parkinson disease with orthostatic hypotension from the Parkinsonian form of multiple system atrophy. Clin Auton Res 2015;25:61-67). About 1/3 of PD patients, most MSA patients, and all PAF patients have neurogenic orthostatic hypotension (OH). In a prospective cohort study we compared long-term survival in these synucleinopathies. We found that survival depends on the particular disease, with the risk of death greater in MSA than in PD+OH and in PD+OH than in PD without OH or in PAF. The analysis also demonstrated differential survivals based on 18F-DOPA putamen and 18F-DA cardiac neuroimaging data alone, regardless of the clinical diagnosis (Goldstein DS, Holmes C, Sharabi Y, Wu T. Long-term survival in synucleinopathies: A prospective cohort study of Parkinson disease, multiple system atrophy, and pure autonomic failure. Neurology 2015 (in press)). We recently published post-mortem neurochemical evidence for decreased putamen aldehyde dehydrogenase (ALDH) activity in both PD and MSA (Cook GA, Sullivan P, Holmes C, Goldstein DS. Cardiac sympathetic denervation without Lewy bodies in a case of multiple system atrophy. Park Rel Dis 2014;20:926-928; Goldstein DS, Sullivan P, Holmes C, Kopin IJ, Sharabi Y, Mash DC. Decreased vesicular storage and aldehyde dehydrogenase in multiple system atrophy. Park Rel Dis 2015;21:567-572). We have sought an in vivo biomarker of central ALDH activity. Decreased ALDH activity should increase CSF levels of indices of DA auto-oxidation with respect to indices of DA enzymatic oxidation. We published previously that PD and MSA involve decreased CSF levels of DOPAC, the main deaminated metabolite of DA. To assess DA auto-oxidation we developed and applied an assay method for measuring cysteinyl-DA (Cys-DA) simultaneously with DOPAC. Preliminarily, CSF Cys-DA:DOPAC is about twice as high in PD and MSA as in controls. Elevated CSF Cys-DA:DOPAC may provide an in vivo biomarker of decreased central ALDH activity in parkinsonian disorders. In a collaborative study with Dr. Alessandro Stefani (University of Tor Vergata, Rome, Italy) we have assayed catechols in CSF from patients with PD, progressive supranuclear palsy (PSP), Alzheimers disease (AD), and controls. Preliminarily, we have found decreased CSF DOPAC in PD and PSP and not in AD, replicating and extending on our previous report based on patients referred to the NIH. In parkinsonian disorders low CSF DOPAC seems to provide a biomarker of central dopaminergic deficiency regardless of the particular pathogenetic mechanism. We are using 11C-methylreboxetine (11C-MRB), a positron-emitting ligand for the cell membrane norepinephrine transporter (NET), as a biomarker to visualize sites of noradrenergic innervation by PET scanning. A potential limitation of 11C-MRB PET scanning is non-specific binding of the tracer. To assess non-specific binding, we are examining effects of NET blockade by desipramine on cardiac 11C-MRB-derived radioactivity and are studying patients who are status post cardiac transplantation and therefore have denervated hearts. In the NINDS PDRisk study (NIH Clinical Protocol 09-N-0010) we are following people with multiple PD risk factors (family history, loss of sense of smell, dream enactment behavior, orthostatic hypotension) to determine whether biomarkers of catecholamine deficiency predict later development of PD. The biomarkers we are focusing on are CSF DOPAC, the putamen:occipital cortex (PUT:OCC) ratio of 18F-DOPA-derived radioactivity assessed by brain PET scanning, and the interventricular septal myocardial concentration of 18F-DA-derived radioactivity assessed by thoracic PET scanning. As of this report, 131,084 people have visited the protocol-specific PDRisk website, 3,030 have entered their risk factor data, 371 have been flagged as eligible at the website, and 78 have come to the NIH Clinical Center and have been accrued. Of the 78 accrued at risk participants, 35 have had confirmation of all their risk factors. Of the 35, 3 already had PD at the time of screening and were not studied further, and 32 screened participants have been invited back for inpatient biomarkers testing. Of the 32, 29 have had data obtained for all three biomarkers. Of the 29, 16 (55%) have had at least one positive biomarker, and of these 4 (25%) so far have developed PD (Lewy body dementia in 1 patient). None of the 13 accrued subjects with confirmed risk factors but without positive biomarkers has developed PD. Under NIH Clinical Protocol 03-N-0004 we are obtaining skin biopsy specimens from patients with different forms of alpha-synucleinopathy. In collaboration with extramural Associate Investigators we are testing whether alpha-synuclein, tyrosine hydroxylase, or DA-beta-hydroxylase immunostaining provides pathophysiologically relevant biomarkers.